SpringerBriefs in Molecular Science Green Chemistry for Sustainability Series Editor Sanjay K. Sharma For furthervolumes: http://www.springer.com/series/10045 Mika Sillanpää Thuy-Duong Pham • Reena Amatya Shrestha Ultrasound Technology in Green Chemistry 123 MikaSillanpää Reena Amatya Shrestha Laboratory ofGreen Chemistry Department of Civiland Environmental LUT Facultyof Technology Engineering Lappeenranta University ofTechnology LehighUniversity Patteristonkatu 1 13E.Packer Ave 50100Mikkeli Bethlehem 18015 Finland USA e-mail: Mika.Sillanpaa@lut.fi e-mail: [email protected] Thuy-Duong Pham Laboratory ofGreen Chemistry LUT Facultyof Technology Lappeenranta University ofTechnology Patteristonkatu 1 50100Mikkeli Finland e-mail: duong.pham@uku.fi ISSN 2191-5407 e-ISSN 2191-5415 ISBN 978-94-007-2408-2 e-ISBN978-94-007-2409-9 DOI 10.1007/978-94-007-2409-9 SpringerDordrechtHeidelbergLondonNewYork (cid:2)TheAuthor(s)2011 Nopartofthisworkmaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorby anymeans,electronic,mechanical,photocopying,microfilming,recordingorotherwise,withoutwritten permissionfromthePublisher,withtheexceptionofanymaterialsuppliedspecificallyforthepurpose ofbeingenteredandexecutedonacomputersystem,forexclusiveusebythepurchaserofthework. Coverdesign:eStudioCalamar,Berlin/Figueres Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Contents Ultrasound Technology in Green Chemistry. . . . . . . . . . . . . . . . . . . . 1 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 Ultrasound: Background Overview. . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Water Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1 General Aspects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2 Improving Disinfection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.3 Intensifying Electrocoagulation . . . . . . . . . . . . . . . . . . . . . . . . 9 3.4 Enhancing Membrane Filtration. . . . . . . . . . . . . . . . . . . . . . . . 9 4 Sludge Stabilization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5 Sediment and Soil Remediation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.1 Heavy Metals Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.2 Organic Decontamination. . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5.3 Ultrasonication as Assistant Process in Organic Contaminated Soil Remediation. . . . . . . . . . . . . . . . . . . . . . . . 13 6 Air Pollution Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 7 Environmental Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 7.1 Assisting Microwave Digestion. . . . . . . . . . . . . . . . . . . . . . . . 17 7.2 Assisting Solvent Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . 17 8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 v Ultrasound Technology in Green Chemistry Abstract Aspartofanewandrapidlygrowingfieldofstudy,theapplicationsof ultrasound in green chemistry and environmental applications have a promising future. Compared to conventional methods, ultrasonication can bring various benefits, such as environmental friendliness (no toxic chemicals are used or pro- duced),costefficiency,andcompact,on-sitetreatment.Besidesanoverviewofthe ultrasonicbackground,thispapersummarizesthemainfindingsandinnovationsof recentstudiesthathavebeenusingultrasoundinenvironmentalanalysis,waterand sludge treatment, and soil andsedimentremediation, as well asair purification. Keywords Ultrasound (cid:2) Environmental analysis (cid:2) Water treatment (cid:2) Sludge stabilization (cid:2) Soil remediation (cid:2) Air purification (cid:2) Green chemistry 1 Introduction Ultrasound refers to inaudible sound waves with frequencies in the range of 16 KHz–500 MHz,above the upperlimitofhumanhearing.It can betransmitted through any elastic medium including water, gas-saturated water, and slurry. Ultrasound has been used for diverse purposes in many different areas (Fig. 1). Intermsoffrequency,ultrasoundcanbecategorizedintotwomainstrands:(1) highfrequency(2–10 MHz)—lowpowerdiagnosticultrasound,involvingmedical imaging,non-destructivetesting,and(2)lowtomediumfrequency(20–1000 kHz) frequency—high power ultrasound, involving other applications in industry, nanotechnology, ultrasonic therapy and sonochemistry. Among these various utilizations, this paper will focus on the uses of ultrasound in the main areas of environmentalscienceandtechnologyrelevanttogreenchemistry,fromwaterand sludge treatment, soil and sediment remediation, and air purification to environ- mental analysis (Fig. 2). M.Sillanpääetal.,UltrasoundTechnologyinGreenChemistry, 1 SpringerBriefsinGreenChemistryforSustainability, DOI:10.1007/978-94-007-2409-9_1,(cid:2)TheAuthor(s)2011 2 UltrasoundTechnologyinGreenChemistry Surface cleaning Medical scanning Ultrasonictherapy Mining processing Industrial welding Food technology ULTRASOUND Material science Non-destructive Nanosynthesis testing (nanotechnology) Environmental applications Fig.1 Diverseapplicationsofultrasound Environmental analysis - Assisted microwave digestion - Assisted solvent extraction Soil & sediment remediation - Removal of heavy metals - Decontamination of organics - Enhancing advanced Environmental Applications ofUltrasound oxidative/electrokinetic soil remediation processes Air purification Water treatment Sludge treatment - Agglomeration of - Decontamination - Stabilization particles - Improved disinfection, - Dewatering - Intensified electrocoagulation - Enhanced membrane filtration Fig.2 Ultrasoundinenvironmentalapplications Although ultrasonic applications in environmental areas are still in lab-scale and developing stage, they are increasing rapidly and attracting more and more interest because of many advantages they offer: environmental friendliness (no toxic chemicals are used or produced), low energy demand, and compact and transportable method that can be used on-site. Environmental remediation by ultrasonicationisinvolvedmostlyinorganicpollutantdestruction,throughthermal decomposition (pyrolysis) and the formation of oxidative species, like hydroxyl radicals, which enhance the mineralization of pollutants. Moreover, in soil treat- ment, ultrasonic waves increase the porosity of the soil and percolation rate, thus accelerating desorption, and facilitating the removal of entrapped contaminants. 1 Introduction 3 Fig.3 Threereactionzones Bulk solution media inthecavitationprocess Interfacial region T P ~ Cavity interior ~ 200 Gas phase 300 0 K P ~ 1000 atm atm T ~ 5000 K Gas-Liquid T ~ 300 K P ~ 1 atm On the other hand, ultrasound applied in environmental analysis also provides benefits such as shorter time, simplified procedure, and higher purity of the final product. In this book, we have updated our earlier work with the most recent developments (Pham et al. 2009a, b). 2 Ultrasound: Background Overview Ultrasound, like any sound wave, is propagated via a series of compression and rarefactionwavesinducedinthemoleculesofthemediumthroughwhichitpasses. Compression cycles push molecules together, while expansion cycles pull them apart. At sufficiently high power, the rarefaction cycle may exceed the attractive forcesofthemolecules oftheliquid,andcavitation bubbleswillform.Cavitation bubble collapse is a remarkable phenomenon induced throughout the liquid. Cavitational collapse produces intense local heating (*5000 K) and pressures (*1000 atm) with very short lifetimes, implying the existence of extremely high heatingandcoolingrates([109K/s).Ithasbeenshownthattransientsupercritical waterisobtainedduringthecollapseofcavitationbubblesgeneratedsonolytically (Hoffmann et al. 1996). Acoustic cavitation provides a unique interaction of energy and matter, and ultrasonic irradiation of liquids causes high energy chemical reactions to occur (Suslick 2006). According to Adewuyi (2001), so far four theories have been proposed to explain the sonochemical events: ‘‘hot-spot’’ theory, ‘‘electrical’’ theory, ‘‘plasma discharge’’theory,and‘‘supercritical’’theory.Thesehaveledtoseveralmodesof reactivity being proposed: pyrolytic decomposition, hydroxyl radical oxidation, plasma chemistry, and super critical water oxidation. Generally, most studies in environmental sonochemistry have adopted the ‘‘hot-spot’’ concepts to explain experimental results. In the hot-spot model (Adewuyi 2001), three regions are postulated (Fig. 3): (1) a hot gaseous nucleus, (2) an interfacial region, and (3) a bulk solution at ambient temperature. Reactions involving free radicals can occur withinthecollapsingbubble,attheinterfaceofthebubble,andinthesurrounding liquid. 4 UltrasoundTechnologyinGreenChemistry Within the center of the bubble, high temperatures and pressures generated during cavitation provide the activation energy required for bond breakage, dis- sociation of solvents and other vapors or gases, leading to the formation of free radicals or excited species. The radicals generated either react with each other to form new molecules and radicals or diffuse into the bulk liquid to serve as oxidants. The second reaction site is the liquid shell immediately surrounding the imploding cavity, which has been estimated to heat up to approximately 2000 K during cavity implosion. In this solvent layer surrounding the hot bubble, both combustion and free-radical reactions (involving (cid:2)OH derived from the decom- position of H O) occur. Reactions here are comparable to pyrolysis reactions. 2 Pyrolysis in the interfacial region is predominant at high solute concentrations, whileatlowsoluteconcentrations,free-radicalreactionsarelikelytopredominate. It has been shown that the majority of degradation takes place in the bubble-bulk interface region. In the bulk liquid, no primary sonochemical activity takes place, although subsequent reactions with ultrasonically generated intermediates may occur. A small number offree radicals produced in the cavities or at the interface may move into the bulk-liquid phase and react with the substrate present there in the secondaryreactionstoformnewproducts.Dependingontheirphysicalproperties andconcentrations,moleculespresentinthemediumwillbeburnedinclosetothe bubble (pyrolysis) or will undergo radical reactions. Thesechemicaleffects(sonochemistry)explainedaboveareutilizedinmostof the ultrasonic applications in environmental remediation, especially in organic decontamination. In addition to that, the physical (mechanical) effects of ultra- sound are also useful in some environmental applications like air purification, sludge dewatering, and metal leaching. Studies that applied ultrasound in envi- ronmentalscienceandengineering with thefocus onthe mostrecent ones willbe summarized and discussed in more detail in the next sections of this book. 3 Water Treatment Inwatertreatmenttechnology,theapplicationsofultrasound(ultrasonication)can be useful in various processes like organic decontamination, disinfection, elec- trocoagulation, and membrane filtration. 3.1 General Aspects Due to the cavitation phenomenon, the formation of free radicals and high localized temperatures and pressures, ultrasonic irradiation (ultrasonication) appears to be an effective method for the destruction of hazardous organic 3 WaterTreatment 5 compounds in water (Hoffmann et al. 1996; Joseph et al. 2000). The beneficial effect of ultrasonication on the removal of several target compounds from aqueous solutions has been demonstrated in many studies. These compounds includephenol(Enterazietal.2003),chlorophenols,nitrophenols,aniline(Emery etal.2003;Teoetal.2001;Jiangetal.2002a,b;Papadakietal.2004;Goskonda et al. 2002; Wang et al. 2011), trichloroethylene (Drijvers et al. 1996), per- chloroethylene (Saez et al. 2011), ethylbenzene (Visscher et al. 1997), chloro- benzene (Dewulf et al. 2001), cationic surfactant laurylpyridinium chloride (Singla et al. 2011), chloronaphthalene (Jiang et al. 2002a, b), polychlorinated biphenyls, pesticides, polycyclic aromatic hydrocarbons, azobenzene, textile dyes (Joseph et al. 2000, Tezcanli-Guyer and Ince 2003), organophosphate pesticide parathiom (Yao et al. 2010), carbofuran (Hua and Pfalzer-Thompson 2001), ni- troaromatics (Abramov et al. 2006), hydrazine (Nakui et al. 2007), diclofenac (Naddeo et al. 2010), polyaromatic hydrocarbons naphthalene, phenanthrene and pyrene (Manariotis et al. 2011), and detergents and surfactants (Adewuyi 2001, Sister and Kirshankova 2005, Abu-Hassan et al. 2006, Belgiorno et al. 2007). Among these various organic contaminants, phenol and phenolic compounds are the most widely investigated. Many studies on sonodegradation of phenolic compounds are summarized carefully in two interesting reviews of Kidak and Ince (2006) and Gogate (2008). In general, the optimum range for the frequency liesbetween200and540 kHz,whilethebestpHisintheacidregion(Kidakand Ince 2006). Studying the effect of pH, Jiang et al. (2002a, b) concluded that the pH of a solution plays an important role in the rate of polar aromatic compound degra- dation by sonolysis, because it affects the charge of the substances (negatively charged under alkaline conditions like 4-nitrophenol, or positively charged at acidic pH like aniline). For these hydrophilic compounds, the neutral species are moreeasilydiffusedtoandaccumulatedatthehydrophobicinterfaceofliquid–gas bubbles in comparison with their corresponding ionic forms. Thus, the rate of 4-nitrophenol degradation decreases with increasing pH, while the rate of aniline destructionexhibitsamaximumunderalkalineconditions.Theultrasonicinduced formationofH O isalsoaffectedbythepHastheyieldofH O hasamaximum 2 2 2 2 at a pH of approximately 3 and decreases with increasing pH (Jiang et al. 2002a, b). Ultrasonic irradiation of carbofuran (C H NO ) was performed at 16 and 12 15 3 20 kHzbyHuaandPfalzer-Thompson(2001)showingthattherateofcarbofuran decomposition increased with higher power density applied (1.65–5.55 W/mL), lower initial carbofuran concentrations (25 lM vs. 130 lM), and when sparging with an Ar/O mixture. 2 Low frequency at 20 kHz has also been used for sonodegradation of linear alkylbenzene sulfonate (LAS) solutions (Abu-Hassan et al. 2006). 20 kHz ultra- sound demonstrated a capability of degrading the sodium dodecylbenzene sulfo- nate (SDBS, a representative LAS molecule). However, the complete mineralisation may not be possible. Degradation rates increased with increasing power and decreasing temperature, and the volume of samples.